Developer composition for penetrant inspection

ABSTRACT

Dry developer composition in powder form for use in penetrant inspection of surface flaws in bodies, consisting essentially of alumina, silica, talc and titanium dioxide. The resulting powder developer is particularly effective when applied to a surface following application of a fluorescent penetrant, to provide bright fluorescent indication of surface flaws when inspected under fluorescent illumination.

United States Patent [1 1 Molina 1 1 DEVELOPER COMPOSITION FOR PENETRANT INSPECTION [75] Inventor: Orlando G. Mollna, Westminster.

Calif. [73] Assignee: Air Products and Chemicals, Inc., Allentown, Pa.

[22] Filed: Dec. 27, 1971 [21] Appl. No.: 212,799

[52] US. Cl. 252/408, 250/71 T [51] Int. Cl C09k 3/00 [58] Field of Search 250/71 T; 252/408 [56] References Cited UNITED STATES PATENTS 2,806,959 9/1957 Forest et al. 250/71 T [451 Apr.-9, 1974 3.279.243 10/1966 Molina 250/71 T 3.303.043 2/1967 Halpaap et a1 3.624.397 I 1/1971 Honeycutt ct a1 250/71 T Primary ExaminerJames W. Lawrence Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-James C. Simmons. Esq.

[5 7 ABSTRACT 7 Claims, No Drawings DEVELOPER COMPOSITION FOR PENETRANT INSPECTION This invention relates to compositions and procedure for non-destructive testing of bodies composed for example of metal, ceramic or plastic, to detect flaws or cracks in the surface of such bodies, and is particularly concerned with novel dry developer compositions for fluorescent penetrant inspection of flaws in such bodies, when employed in conjunction with fluorescent penetrants, the powder developers of the invention being particularly effective in providing bright fluorescent indications, and having additional important advantages and superior results in comparison with presently known and commerically available powder developers.

ln known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a penetrant composition containing a fluorescent dye and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition is then applied to this part surface. Such developer can be in the form of a light colored powder, which contrasts with the color of the dye and which acts as a wick and causes the liquid penetrant containing the fluorescent dye which was re tained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action, and to bleed" through the developer. The part is then exposed to invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.

In order to increase the sensitivity of fluorescent penetrant inspection methods, it has been sought to increase the brightness of fluorescence of the fluorescent penetrant dye and to increase the contrast between the light received from the fluorescent penetrant indicator and from adjacent areas of the test part.

Various developer compositions for penetrant inspection of surface cracks and flaws have heretofore been employed. Thus, for example, US. Pat. No. 2,806,959 discloses finely powdered silica, preferably admixed with talc; US. Pat. No. 2,848,421 discloses a composition comprising silica aerogel and talc; US. Pat. No. 2,420,646 discloses use of diatomaceous earth or talc; U.S. Pat. No. 2,920,203 discloses the use of French talc and light magnesium carbonate; and US. Pat. No. 3,1 17,227 discloses the combination of diatomaceous earth and silica aerogel.

However, most of the developer compositions of the prior art have the disadvantage that they tend to fluoresce particularly in the blue region, when the surface of the body to which the fluorescent penetrant and developer composition have been applied is inspected under fluorescent light. This is a disadvantage when employing fluorescent penetrants, since it reduces the amount of contrast between the fluorescent penetrant indication and the surrounding area covered by the developer composition, and hence in effect reduces the brightness of fluorescence of the fluorescent dye.

Further, many of the prior art developer compositions tend to agglomerate and cake and hence this reduces their sensitivity to penetrant inspection of very small cracks or microcracksin the surface being tested.

Further, certain of the prior art developer compositions are not'compatible with certain metals such as titanium and high nickel alloys which are used particularly in the aerospace industry, because such compositions contain elements or components such as chlorine and sulfur, so that the resulting composition has a low pH when contacted by the liquid penetrant.

Also, some of the prior art compositions are toxic and hence present hazards in handling.

It is accordingly the object of. the present invention to provide dry developer compositions for fluorescent penetrant inspection of the surface flaws of bodies,

which provides bright fluorescence and sharp contrast between the light emitted from the fluorescent penetrant indicating the location and nature of cracks and imperfections in the body, and the adjacent areas of the partyand which have other important advantages in,- cluding light free-flowing characteristics, compatibility with structural materials such as metals and alloys thereof, and which are essentially nontoxic and relatively inexpensive.

The above objects are achieved according to the invention by the provision of a dry powdered developer composition for penetrant inspection of surface flaws, which consists essentially of four components, namely, (1) alumina, (2) silica, (3) talc,,and (4) titanium dioxide. The respective components of the composition preferably are in powder form, the particles of such respective components being of small size, and preferably such components are employed in certain proportions, as pointed out in detail hereinafter. The dry powder developer formulation of the invention has the unique characteristics and advantages of being unusually nonfluorescent under black light (fluorescent) illumination, causing the fluorescent penetrant to fluoresce brightly in relation and in contrast to the surrounding white powder developer, and such developer composition is unusually light, fluffy and free flowing and readily passes into minute cracks or microcracks, as well as large cracks, in the surface of the body. Further, the developer composition of the invention is essentially neutral, having a pHof the order of about 7, and accordingly is highly compatible with all metals and metal alloys. Moreover, the dry powder developer composition hereof is essentially nontoxic and is accordingly readily handleable by personnel, and is economical.

The first essential component-of the developer composition of the invention is alumina, preferably employed in an extremely flne powder form having a particle size ranging from about 0.007 to about 0.050 mlcron. A particularly effective form of alumina for use in the developer composition of the invention is a fumed alumina of varying crystalline forms consisting predominantly of the gamma modification. A commerically available form of alumina of this type found especially effective is the material marketed as Cab-O-Grip, also known as Alon, by Cabot Corporation of Boston, Mass. The latter material is an extremely light, fluffy and fine material, each gram of which has a surface area of about square meters. This white alumina powder particularly imparts high fluorescent brightness to the fluorescent penetrant contacting the composition, and is a positively charged powder which functions also as a binder for the other components of the formulation.

The second essential component of the invention composition is silica, employed also preferably in fine powder form of particle size ranging from about 0.007 to about 0.050 micron (about 70 to about 500 angstroms), and is an extremely fluffy, snow-white powder of extremely low bulk density. A commerically available form of this component is marketed as Cab-O-Sil M-S by Cabot Corporation. As in the case of the preferred form of alumina, marketed as Cab-O-Grip noted above, the Cab-O-Sil has an enormous external area, one gram of Cab-OSil M-S having about 400 square meters of surface area. Cab-O-Sil M-5 is a submicroscopic fire-dry fumed silica different in structure from precipitated silicas or silica gels. This white silica powder imparts free-flowing, non-caking properties to the overall powder developer composition, and also aids in developing bright fluorescent indications of fluorescent penetrants.

The third essential component is talc (which is a magnesium silicate). This material is also a fine white powder of small but irregular particle size. A commercially available material suitable for purposes of the invention is that marketed as Desert Talc Mikro 507, by Desert Minerals, Inc. of Los Angeles, Calif. The latter material is a semi-tremolitic-acicular-platey having a particle size distribution ranging from about to less than l micron, and is essentially a calcium-magnesium silicate. This white powder provides a unique combination of highly irregular particle sizes and shapes, leaving an almost invisible film deposit of fine particles which provides a path for entrapment of fluorescent penetrant which exudes from microcracks in the surface to which the developer is applied. Accordingly, such fine powdery talc adheres to almost any type of surface including very fine or polished surfaces such as polished chrome plating. Due to the irregular particle size content of such talc, it functions as an aid to depositing the developer in varying size cracks.

The fourth essential component of the developer composition is titanium dioxide, also preferably employed as a powder of small particle size. A particularly effective material of this type is that marketed as Cab- O-Ti by Cabot Corporation. This material is a fumed, ultra-fine nonpigmentary titania of high external surface area and small particle size, also ranging from about 0.007 to about 0.050 micron. Such titanium dioxide in the form of a white powder functions as an ultraviolet filter which has the important characteristic of rendering the other above-noted powder components of the developer colorless under fluorescent or black light illumination. All of the other above-noted components of the developer composition possess -a natural fluorescence to a lesser or greater degree when exposed to black light illumination which is undesirable because it interferes with and reduces the brightness of the fluorescent indication produced by the penetrant. This undesirable characteristic of the above white powders of alumina, silica and tale is accordingly essentially avoided and such powders rendered essentially nonfluorescent by the presence of the titanium dioxide. Further, it has been found that the other functions of the other three components of the composition, including provision of fluffiness, free flowing and non-caking properties, adherence to the object surface, and ability to pass into varying size cracks including microcracks, are enhanced, and fluorescent brightness of the fluorescent penetrant indications is further enhanced, by the presence of the titanium dioxide.

It is accordingly seen that the components of the developer composition hereof, particularly the titanium dioxide, function in a synergistic manner to obtain the improved results and advantages noted above.

It has been found that in order to obtain effective results with the developer composition of the invention, the components thereof should be employed in certain proportions. Thus, the alumina is employed in a range of about 25 percent to about percent, preferably about 30 percent to about 60 percent; the silica in an amount ranging from about 2 percent to about 25 percent, preferably about 4 percent to about 15 percent; the talc in an amount of about 25 percent to about 60 percent, preferably about 30 percent to about 55 percent; and the titanium dioxide in an amount ranging from about 3 percent to about 25 percent, preferably about 6 percent to about 15 percent. The above-noted percentages are based on the total weight of the composition. Preferably, substantial proportions of alumina and talc are employed, and minor proportions of silica and titanium dioxide.

Illustrative examples of developer compositions according to the invention, but not in limitation thereof, are set forth in the table below, the amounts of the respective components being expressed in terms of per cent by weight.

weight) Examples (percent by Particularly effective developer compositions according to the invention, for fluorescent penetrant inspection, are those of Examples 1, 2, 5, 7 and 10 of the above table.

The fluorescent penetrant composition which can be employed in conjunction with the novel developer composition of my invention, can comprise a fluorescent dye and a liquid vehicle for such dye. Thus the fluorescent penetrant composition can be an oil base, surfactant base, solvent base or water base penetrant composition. The penetrant vehicle should be a liquid which is itself substantially non-fluorescent and having good wetting properties and the ability to penetrate fine surface cracks and imperfections readily. Satisfactory penetrant vehicles include, for example, petroleum solvents, kerosene, a mineral oil or spirit, or mixtures thereof, light fuel oils, and the like. Other solvents include, for example, ketones, esters and organic acids. The penetrant may also contain an emulsifying agent which renders thepenetrant composition wateremulsiflable. Such emulsifying agents may be, for example, oil-soluble soaps, detergents, and the like. The amount of fluorescent dye incorporatedin the penetrant composition may range from about 0.05 to about 15% by weight of such composition.

However, it has been found that the developer composition of the invention is particularly effective whencation Ser. No. 68,475, filed Aug. 31, 1970 now abandoned, which is a continuation of Ser. No. 655,752, filed July 25, 1967. The dye penetrant composition thereof comprises a suitable bleeding fluorescent dye and a stable lactam solvent for said dye, such as gamma-butyrolactam, and particularly N-methyl-2- pyrrolidone. Various types of fluorescent dyes can be employed including for example the dye marketed as Fluorol 7GA as well as other fluorescent dyes such as those marketed as Calcofluor Yellow, Azosol Brilliant Yellow 6GP, Rhodanine B, Rhodanine 6GDN, Calcofluor White RW, Blancophor White AW, Auramine and Eosine G.

The fluorescent penetrant composition according to my above copending application and particularly containing N-methyl-Z-pyrrolidone as vehicle, permits rapid cleaning of dye penetrant from the specimen surface by the application of water thereto without the intermediate use of emulsifiers or the like. Also, if desired, a surfactant can be incorporated which functions to more readily remove excess dye together with excess dye vehicle from the surface upon application of water. Such surfactant can be for example a nonionic detergent such as Tergitol Nonionic NPX of Union Carbide, which is understood to be a nonyl phenyl polyethylene glycol ether. Further, the penetrant composition of my above copending application can include a waterinsoluble solvent such as isobutyl heptyl ketone. An exemplary improved fluorescent penetrant composition of my above copending application has the following composition.

EXAMPLE 12 In employing my novel developer composition according to the invention, in a fluorescent penetrant inspection process, the process broadly comprises applying to the surface of a specimen a liquid penetrant of the above-described type, comprising a fluorescent dye and a liquid vehicle for such dye, removing excess liquid penetrant from the surface while leaving liquid penetrant in any cracks or flaws therein, applying to the surface a developer composition according to the invention, removing excess developer composition from the surface, and inspecting the surface of the body under fluorescent light to locate any cracks in said surface as indicated by fluorescent emission from the dye drawn into the developer composition in the vicinity of such cracks.

More particularly, in carrying out such method, if necessary, the part or surface to be inspected first can be suitably prepared as for example by suitably cleaning and drying the specimen.

The liquid fluorescent penetrant is then applied to the test specimen, e.g., by. dipping same into a bath of the penetrant, or the penetrant can be poured or sprayed onto the surface of the test specimen. The dye penetrant composition is maintained on the surface of the test body or specimen for a period sufficient to permit the composition to penetrate the cracks and imperfections in the part surface, e.g., for about I to about 60 minutes.

The fluorescent penetrant composition is then removed or washed off the surface of the part being tested, without being removed from the openings of the surface cracks or flaws. This can be accomplished by any suitable means such as by wiping with a cloth, or a solvent impregnated cloth, or withwater where the penetrant composition has been rendered water emulsifiable by addition thereto of an emulsifying agent. Thus for example the excess fluorescent penetrant of my above copending application can be removed from the test specimen by application of a sprayed mixture of air and water.

The novel developer composition of the invention is then applied to the surface of the test specimen, as for example by dipping the specimen into the developer composition, or sprinkling or dusting the powder developer onto the surface of the specimen. The powdery developer. composition absorbs the liquid penetrant and fluorescent dye therein, contained in the cracks and flaws of the part surface, by capillary action and forms a fluorescent smear or indication adjacent the crack openings. As an important feature of the invention, as described above, when the test body is exposed to fluorescent or black light, the contrast between the fluorescent streaks or smears produced by the fluorescent penetrant in the mouth of the cracks and flaws in the test body, and the surrounding background of the white developer, is substantially enhanced, producing brillant fluorescent indications.

The following are examples of practice of the invention employing the novel developer composition thereof.

EXAMPLE 13 The fluorescent dye penetrant of Example 12 above, according to my above copending application, was applied as by brushing, to a chromium-plated brass test panel containing cracks 0.00002 to 0.0001 inch in width, closely distributed over its entire surface, and the penetrant was maintained on such surface for about 1 to about 2 minutes. Excess dye penetrant was then removed from the surface of the test panel by spraying a mixture of air and water over the panel surface.

Half of the test panel surface to which the dye penetrant was applied was then covered with the dry developer composition of Example 1 above, and the other half of the surface of the test panel to which dye penetrant was applied was covered with a commerically available dry developer composition. The developers were permitted to dwell over the test panel for a period of 2 minutes.

Excess developer composition was then carefully removed from both half surfaces of the test panel by means of a gentle air blast.

The panel was then placed under black light (fluorescent) illumination and the respective half surfaces viewed in such illumination. It was observed that the half side of the panel which had been treated with the dry developer composition of Example l according to the present invention disclosed fluorescent indications from numerous readily defined ,microcracks therein. Observation of the half side or surface of the panel which had been treated with the above-noted commercial developer could not detect any fluorescent emissions from the microcracks in the surface, and hence such microcracks could not be located.

EXAMPLE 14 The procedure of Example 13 was essentially repeated but employing an aluminum test panel in place of the chromium-plated test panel of Example 13, and employing the dry developer composition of Example 2 in place of the dry developer of Example 1.

Results similar to those of Example l3 were obtained.

EXAMPLE [5 The procedure of Example 13 was essentially followed, except employing a titanium test panel in place of the chrome-plated panel of Example 13, and employing the dry developer composition of Example 7 in placeof the dry developer composition of Example 1.

Results similar to those of Example 13 were obtained.

EXAMPLE 16 The procedure of Example 13 was again essentially followed, but employing a steel test panel in place of the chrome-plated panel of Example 13, and employing the dry developer composition of Example in place of the dry developer of Example 1.

Comparable results were obtained to those of Example l3.

The dry developer composition of the invention can be employed in conjunction with a fluorescent penetrant for penetrant inspection of cracks and microcracks as small as 0.00002 inch, or less, wide in the surface of bodies of various materials, including, in addition to metals and alloys thereof, such as titanium, steel, copper and aluminum, ceramics, glass, plastics and rubber.

From the foregoing, it is seen that the invention provides a novel dry developer composition for fluorescent penetrant inspection of flaws in bodies, of improved properties and advantages over known and presently available eommerical developers.

While I described particular embodiments of my in- 8 vention for the purpose of illustration within the spirit of the invention, it will be understood that the invention is not to be taken as limited except by the scope of the appended claims.

l claim 1. A non-fluorescing, free-flowing, dry powdered developer composition for penetrant inspection of surface flaws in a workpiece consisting essentially of: 25 to 60 percent by weight alumina, 2 to 25 percent by weight silica, 25 to 60 percent by weight talc, and 3 to 25 percent by weight titanium dioxide.

2. A dry developer composition as defined in claim 1, said alumina being fumed alumina, said silica being fumed silica, and said titanium dioxide being fumed titania, and said talc being of particle size ranging from about 15 to less than about 1 micron.

3. A dry developer composition as defined in claim 1, wherein said alumina, said silica, and said titanium dioxide are in finely divided form having a particle size in the range of 0.007 to 0.050 micron, said alumina having a surface area of 100 square meters per gram, and said silica having a surface area of 400 square meters per gram.

4. A dry developer composition as defined in claim 1, consisting essentially of about 30 to about 55 percent powdered alumina, about 4 to about 15 percent powdered silica, about 30 to about 55 percent powdered talc and about 6 to about 15 percent powdered'titanium dioxide, by weight.

5. A dry developer composition as defined in claim 2, consisting essentially of about 30 to about 55 percent alumina, about 4 to about 15 percent silica, about 30 to about 55 percent talc and about 6 to about l5 percent titanium dioxide, by weight.

6. A dry developer composition as definedin claim 2, consisting essentially of about 35 percent alumina, about 4 percent silica, about 52 percent talc and about 9 percent titanium dioxide, by weight.

7. A dry developer composition as defined in claim 2, consisting essentially of about 42 percent alumina, about 5 percent silica, about 42 percent talc and about 11 percent titanium dioxide, by weight. 

2. A dry developer composition as defined in claim 1, said alumina being fumed alumina, said silica being fumed silica, and said titanium dioxide being fumed titania, and said talc being of particle size ranging from about 15 to less than about 1 micron.
 3. A dry developer composition as defined in claim 1, wherein said alumina, said silica, and said titanium dioxide are in finely divided form having a particle sIze in the range of 0.007 to 0.050 micron, said alumina having a surface area of 100 square meters per gram, and said silica having a surface area of 400 square meters per gram.
 4. A dry developer composition as defined in claim 1, consisting essentially of about 30 to about 55 percent powdered alumina, about 4 to about 15 percent powdered silica, about 30 to about 55 percent powdered talc and about 6 to about 15 percent powdered titanium dioxide, by weight.
 5. A dry developer composition as defined in claim 2, consisting essentially of about 30 to about 55 percent alumina, about 4 to about 15 percent silica, about 30 to about 55 percent talc and about 6 to about 15 percent titanium dioxide, by weight.
 6. A dry developer composition as defined in claim 2, consisting essentially of about 35 percent alumina, about 4 percent silica, about 52 percent talc and about 9 percent titanium dioxide, by weight.
 7. A dry developer composition as defined in claim 2, consisting essentially of about 42 percent alumina, about 5 percent silica, about 42 percent talc and about 11 percent titanium dioxide, by weight. 